Photographic Process of Positive PS Plate (1)

The PS plate that has been coated with a photosensitive layer in advance is subjected to processes such as exposure, development, removal of dirt, and gluing to form a printing plate for printing. In the positive PS version, the exposed photosensitive layer undergoes a photodecomposition reaction and is dissolved by the developer solution to be removed from the plate surface. After the adhesive layer is coated, a stable hydrophilic blank portion is formed; and the unexposed photosensitive layer is left in the The plate has lipophilicity and constitutes part of the image (Figure 1 ).

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Fig. 1    Positive PS process

       One, exposure

The photosensitive positive layer of the positive and PS plates is sealed and placed in a special printing machine. After vacuum extraction, the light source of the printing machine is turned on, and the photosensitive layer of the non-image part is lighted under light irradiation. Decomposition reaction, this process is called exposure, also known as printing.

1. Original outlet quality

PS version of the sand fine, high resolution, with a good reproduction of the tone and reproduction of the network. In order to make full use of this advantage of the PS version, there are certain requirements for the dot density and dot finish of the original used in the printing.

The original version of the PS plate was usually made by electronic scanning, photography, or laser photography. In the original production process, since the gamma value of the photographic film is low, when the exposure, development or thinning is excessive, a soft dot having a low density value or an activity having a small edge density value and a large central density value will be formed. With such an original printing plate, a slight increase or decrease in the amount of exposure will cause a large reduction or increase in the area of ​​the printing plate's Internet site, thus affecting the reproducibility of the PS plate to the dot (see FIG. 2 ). Therefore, the dots on the original plate used for printing should be hard dots with high density values, uniform edges and center density, and smooth peripheral edges. Generally, the dot density value is required to be 3.0 or higher (the density value of the field version should be higher). The exposure latitude of rigid outlets is relatively large. Even if there is a slight change in exposure, the dot area on the printing plate will not change too much. The quality of the printing plate is relatively stable.

For the original printing plate, the surface is also required to be clean, no scratches, pinholes, and glue marks of the stitched image.

Fig. 2 Reproducibility of soft and hard dots